The operating firmware of a portable flash memory storage device is stored in the relatively large file storage memory, which is non executable. It is logically parsed into overlays to fit into an executable memory. The overlays can be of differing sizes to organize function calls efficiently while minimizing dead space or unnecessarily separating functions that should be within one or a group of frequently accessed overlays. For an overlay having functions that require data allocation, the data allocation can cause eviction. This self eviction is avoided altogether or after initial runtime.